1. Field of the Invention
This invention relates to a constant velocity joint, specifically a plunging type tripod type constant velocity joint. Generally, the constant velocity joint is a kind of a universal joint capable of transmitting torque at constant velocity even if there is an angle between two shafts, on the driving and driven sides, when joined together. The plunging type is designed to allow relative axial displacement between two shafts by the plunging of the joint, while the tripod type uses a tripod member having three radially projecting trunnions and adapted to be joined to one shaft, and an outer joint member in the form of a hollow cylinder having three axially extending track grooves and joined to the other shaft, the trunnions of the tripod member being received in the track grooves of the outer joint member to effect torque transmission.
2. Brief Description of the Prior Art
The applicants have previously proposed a tripod type constant velocity joint designed for further reduction of induced thrust and slide resistance and for stability (Japanese Patent Laid-Open Publication 2000-320563). FIGS. 6 and 7 show a portion of such tripod type constant velocity joint. As can be seen from these figures, a functionally necessary clearance is defined between a roller assembly (32xe2x80x2, 34) and the outer peripheral surface of a trunnion (22) (ag1 less than "PHgr"Ds1). In the assembly step, as soon as the roller assembly (32xe2x80x2, 34) is set on the trunnion 22, the outer joint member (10: see FIG. 1A) is fitted. Therfore, the functionally unnecessary fixing (slipping-off prevention) of the trunnion 22 and the roller assembly (32xe2x80x2, 34) is left unpracticed in the present circumstance.
There may be thought of cases where the slipping-off prevention, which is functionally unnecessary, is required by the user from the standpoint of handling. Particularly, when the drive shaft removed from a vehicle, exceeding the permissible slide range, the rollers may come off. conventionally, as a means for preventing such roller coming-off, for example, a slipping-off preventive circlip is installed at the cup inlet portion of the outer joint member to control the slide or a slipping-off preventive circlip or snap ring is installed at the front end of the trunnion. Each such attempt has problems to be solved. That is, in the former case, there are problems including not only an increase in the number of parts due to the use of circlips but also an increase in weight due to the increased cup length of the outer joint member, while in the latter case, there are problems including an increase in the number of parts due to the use of circlips and snap rings, the increase in the number of parts leading to an increase in costs.
An object of the invention is to prevent the coming-off of the roller assembly without incurring an increase in costs due to the increased number of parts or an increase in weight due to the increased cup length of the outer joint member.
According to an embodiment of the present invention, a constant velocity joint comprises an outer joint member formed with three axial track grooves in the inner periphery and having axial roller guide surfaces on opposite sides of each track groove, a tripod member having three radially projecting trunnions, a roller assembly mounted on each trunnion of the tripod member, the roller assembly being tiltable with respect to the trunnion and having a roller guided along the roller guide surface in a direction parallel with the axis of the outer joint member, the joint being characterized in that a means for preventing the roller assembly from coming off is installed in the vicinity of the front end of the trunnion. Specifically, this means may take the form of projections. By making the relation between the circumscribed circle diameter af1 of the projections and the inner diameter "PHgr"Ds1 of the ring such that af1 greater than "PHgr"Ds1, even if the roller assembly tries to move in the axial direction to come off the trunnion, the ring interferes with the projections, thereby preventing the roller assembly from coming off. It is desirable that the radial projecting amount (af1xe2x88x92"PHgr"Ds1) of the projections be set at about 0.05xe2x88x920.1 mm. This is because if (af1xe2x88x92"PHgr"Ds1) less than 0.05 mm, the coming-off preventing function cannot be developed, while if (af1xe2x88x92"PHgr"Ds1) greater than 0.1 mm, the amount of interference will be large, so that incorporating operation becomes difficult. Further, the lengthwise dimension h of the projections is preferably 0.1-0.5 mm. This is because if h less than 0.1 mm, the coming-off preventing function cannot be developed, while if h greater than 0.5 mm, the amount of interference will be large, so that the incorporating operation becomes difficult.
The roller assembly may comprise the roller and a ring fitted on the trunnion for rotatably supporting the roller. In this case, the projections interfere with the inner diameter of the ring. The ring and roller may be fitted together so that they are relatively rotatable and that they are slide-contactable on their cylindrical surfaces, or rolling elements, such as needle rollers, may be interposed therebetween. At any rate, the ring and the roller are unitized so that they are inseparable as by washers.
The outer peripheral surface of the trunnion may be such that it is straight as seen in a longitudinal sectional view thereof and in a cross sectional view thereof it contacts the inner peripheral surface of the ring in a direction orthogonal to the axis of the joint, and defines a clearance between it and the inner peripheral surface of the ring in the direction of the axis of the joint. Such arrangement allows the roller assembly to oscillate with respect to the trunnion. As for the cross sectional shape of the trunnion, the shape is such that the trunnion contacts the inner peripheral surface of the ring in a direction orthogonal to the axis of the joint and defines a clearance between itself and the inner peripheral surface of the ring in the axial direction of the joint: in other words, the surfaces opposed to each other axially of the tripod member are retracted in the mutual direction, that is, toward the minor diameter sides, away from the imaginary cylindrical surface. A concrete example thereof is an ellipse. However, it is not limited literally to an ellipse, and it is to be understood that generally, it includes what are termed ovals.
Making the cross sectional shape of the trunnion in the shape described above allows the trunnion to tilt with respect to the outer joint member when the joint takes an operating angle, without changing the attitude of the roller assembly. Furthermore, since an osculating ellipse, or an elliptical area of contact, between the outer peripheral surface of the trunnion and the ring approaches a dot from oblongness, the friction moment tending to tilt the roller assembly reduces. Therefore, the attitude of the roller assembly is stabilized all the time, and the roller is held parallel with the roller guide surfaces, so that it rolls smoothly. This contributes to a reduction in slide resistance and hence in induced thrust. Further, there is another merit that the increased section modulus of the root of the trunnion increases the bending strength of the trunnion.
In addition, the roller assembly, which is interposed between the trunnion and the outer joint member, performs the function of transmission of torque. In this kind of constant velocity joint, the direction of transmission of torque is always orthogonal to the axis of the joint; therefore, the transmission of torque is possible in that the trunnion and the ring contact each other in the direction of transmission of torque. And there is no trouble caused in torque transmission even if there is a clearance between them in the axial direction of the joint. In attaching the roller assembly to the trunnion, it is necessary for the roller assembly to ride over the projection, but this can be easily attained since the cross section of the trunnion is elliptic. By elastically deforming the ring by radially inwardly applying an external force P to the roller assembly, the relations af1 less than Dda and b1 less than Ddb hold.
As for the method of forming projections as means for preventing the coming-off of the roller assembly, it may be effected by selectively leaving a non-ground region in the outer peripheral surface of the trunnion, as shown in FIG. 8 or by crimping the front end by plastic working or by beating. As shown in FIG. 11, the projections may be formed by cutting (lathing or grinding). After the roller has been attached to the trunnion, the front end may be crimped by plastic working or beating.